The present invention relates generally to microsurgical equipment and systems, especially those used in ophthalmic surgery. More particularly, the invention relates to a cassette apparatus for collecting substances removed from a surgical situs by suction. The cassette is adapted for removable connection to a control console and provides fast aspiration response time from a single vacuum source.
Present day microsurgical systems for performing ophthalmic surgery typically provide one or more handheld instruments attached to and operated by a control console. The instruments typically are a vitreous cutting probe or a suction cannula. The probe or cannula are usually provided with a hollow needlelike tip through which the substances removed from the surgical situs are suctioned into a removable, throwaway cassette. The control console houses an adjustable vacuum source for providing the aspiration suction to the probe or cannula, and also includes a pneumatic driver system for causing the shearing or rotary cutting action of the probe tip.
In practice, the probe or cannula are coupled through a length of plastic tubing to the cassette collection container and a vacuum is drawn in the container by the variable vacuum source when aspiration is required. One problem encountered in microsurgical systems of this type is that the comparatively slow vacuum rise time in the collection receptacle make it difficult to precisely control the aspiration desired. In eye surgery this is particularly crucial, since aspiration must be precisely controlled to remove only diseased tissue without damaging adjacent healthy tissue. Generally speaking, the ideal aspiration system would have a very fast vacuum rise time and a similarly fast fall time or turn off time. This ideal has been difficult to achieve due to the inertia of the fluid system which includes the aspirator. To an appreciable extent, this inertia is due to the volume of the collection container and the comparatively long time needed to effect a pressure change in that container.
As one solution to the aforementioned vacuum rise time problem, one aspiration system uses a double collection bottle arrangement in which a small bottle is used during aspiration for the rapid response time which the small volume allows. To overcome the problem of having the small bottle fill up too quickly, a second, larger bottle is coupled to the small bottle and a second (frequently more powerful) vacuum source is provided for suctioning the contents of the small bottle into the large bottle as required to prevent overfilling of the small bottle. While generally workable, this two bottle, dual-vacuum system is overly complex, requiring the independent control of two separate vacuum sources. With greater complexity goes a greater likelihood of malfunction, hence, the dual-bottle, dual-vacuum system, leaves room for improvement.
The present invention provides the benefits of a dual-bottle collection system through a much simpler and more reliable arrangement which requires only one vacuum source. The present invention also provides a collection cassette which is less expensive to manufacture. The invention thus offers considerable improvement over prior microsurgical equipment.
Accordingly, the present invention provides a microsurgical apparatus for collecting substances removed from a surgical situs by suction. The invention comprises a fast rise time primary container having a means for selectively applying a vacuum thereto and having an inlet means for communicating with the surgical situs, typically through an aspirating cutting probe or cannula. The invention further comprises a secondary container of a capacity greater than the primary container. Both containers are integrally formed into a unitary, generally boxlike cassette. The containers are disposed so that a given quantity of the substance in the primary container has a greater potential energy than the same quantity of substance has in the secondary container. A first passage communicates between the primary and secondary containers to conduct substances from the primary to the secondary by gravity, thereby eliminating the need for a dual-vacuum system.
To maintain the fast rise time during aspiraion, a first valve is provided which opens and closes the first passage in response to vacuum pressures within the primary container. When vacuum is applied to the primary container, the valve is closed, maintaining the fast rise time of the primary container and preventing the down flush of substance into the secondary container. When the vacuum is removed from the primary container, the valve opens, permitting the automatic down flush or emptying of substances from the primary into the secondary container by gravity. The secondary container is vented to atmosphere while the primary container is provided with a vent valve which selectively opens to vent to atmosphere. This vent valve is opened during times when the aspiration vacuum is removed from the primary container, thereby equalizing the pressure in both containers and permitting rapid flushing from the primary to the secondary container. Preferably the invention employs a vacuum supply valve for selectively applying a vacuum to the primary container and an aspiration inlet valve for opening and closing the aspiration inlet. Both vacuum supply and aspiration inlet valves are arranged for substantially simultaneous operation. The vent valve is arranged for sychronized reverse operation relative to the aspiration inlet and vacuum supply valves. The vent valve is closed when the vacuum supply and aspiration inlet valves are open, and vice versa.